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Mechanically-damaged HVAC ducts: this article describes damaged HVAC ducts due to some mechanical activity such as stepping on a duct and crushing it, or improper and too-aggressive duct cleaning methods that damage duct interior surfaces, liners, or binding resins.

This article series discusses duct system defects such as missing air conditioning cool air supply
or return air registers, undersized air conditioning duct openings, improper cooling duct routing, cooling (or heating) air duct corrosion, leaky air duct connections,
defective heating or cooling ductwork materials such as Goodman gray flex-duct, some Owens Corning Flex-duct, and asbestos-containing air conditioning or heating duct work.

Photo Guide to Damaged HVAC Air Ductwork

Damaged Flex-Duct

At left our photo, provided by reader Steven King, shows the interior of fiberglass-lined flexduct that has been crushed, perhaps by having been stepped-on?

The result is reduced heating or cooling air flow, reduced building occupant comfort, and higher heating or cooling system operation cost.

We were also concerned that the exposed fiberglass in the duct appears to have been mechanically damaged, perhaps by a too-aggressive attempt at duct cleaning that may result in higher levels of airborne fiberglass duct insulation fragments in the building.

Other crimping and blockage or support problems found in flexduct installations are discussed at DUCT ROUTING & SUPPORT.

Damaged blocked combination of fiberglass flex duct & metal ductwork

This photo shows the connection of fiberglass flex duct to a metal HVAC duct component. The fiberglass flex duct has been badly damaged.

As this photograph of duct damage was taken at the same installation as the example above, we suspect that an inexperienced duct cleaner has been at work here.

Rust damage to HVAC air duct systems

The rusted out duct photo at left shows a common return air duct system in some older homes: space between the floor joists was used as an air passage, sometimes also for supply air.

But when the metal sheeting nailed across the floor joist bottoms has rusted out, severe air leaks occur.

In a supply duct the result is higher heating or cooling costs. In a return air duct a hole such as the one shown in our photo can cause unhealthy or unsafe conditions by drawing other unanticipated air into the duct system (in this case next to a crawl space vent we are basically heating outdoor air and blowing it into the living area).

At below right we illustrate the rust (and rodent infestation) found in an in-slab metal spiral air duct. SLAB DUCTWORK - catalogs the functional and environmental problems found when HVAC air ducts are routed in or below floor slabs

Other Duct System Damage Topics are listed in the links listed at the "More Reading" links at the bottom of this article under DUCT SYSTEM & DUCT DEFECTS; some of those links are described below.

Air filter or other item that has been sucked into the duct system will block air flow and can risk a fire if drawn into the blower assembly fan, DIRTY AIR FILTER PROBLEMS are perhaps the most common cause of unsatisfactory airflow in an HVAC system.

Blower Fan: dirty blades on a squirrel cage blower assembly fan significantly reduce the blower fan's ability to move air into the HVAC system from the return-air side as well as reducing its ability to push conditioned air into the occupied space. DIRTY A/C BLOWERS

Fire damper that has become stuck in the closed or partly-closed position interferes with proper airflow through the system FIRE & SMOKE DAMPERS, AUTOMATIC

Flex duct defects: Collapsed sections of flex duct block or stop airflow in either supply or return air systems DUCT ROUTING & SUPPORT

Leaks in the supply air duct system are a very common HVAC duct defect that results in poor heating or cooling air flow. LEAKY DUCT CONNECTIONS

Return air inlets: Return air inlet grilles that are obstructed with dirt, debris, or furniture or that are improperly located or are just too small mean that because the heating or cooling system is "starved for air", the supply air flow into occupied spaces will also be reduced. RETURN AIR REGISTERS & DUCTS

SLAB DUCTWORK - functional and environmental problems found in HVAC air ducts in or below floor slabs

Spiral metal duct work damage (photo at left): rust and collapse when found in floor slabs. See the slab ductwork link just above.

Zone dampers that are stuck partly closed obstruct air supply into that building area, or if stuck "open" when the zone damper should be closed, airflow to other building areas will be reduced. ZONE DAMPER CONTROLS

Damaged or Lost HVAC Duct Insulation

Reader Question: is thi normal wear on the insulation on my duct work? Should I be worried about mold contamination?

Had an insulation question. Hopefully you are able to view the attached pictures. Do you think this is normal wear to the insulation around the
Duct work or should I be concerned about the possibility of mold contamination? - J. 3/31/2014

Reply:

I'm not sure what I'm looking at in your photos but it looks as if fiberglass insulation has been lost around the outside of galvanized metal HVAC ductwork.

If that's so the results are increased operating costs & risk of in-duct condensation and moisture-related problems (mold for example).

Causes of mold growth in HVAC ductwork - mold in air ducts at WHY DOES MOLD GROW in INSULATION? for a discussion of possible mold growth in fiberglass insulation in general.

Generally if I see ducts like this I expect that all of the original installation was on the duct exterior - where it doesn't produce much of a particle hazard to air flowing inside the ducts except in the event of duct leaks in the return air system. (See AIR LEAKS in RETURN DUCTS).

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Question:
Un-lined Flex Ducts Exposes Fiberglass in My Home - is this OK?

I have some pictures that I think you maybe interested and perhaps help others determining what is happening or has happened to the flexduct.

It is similar to the ones above but have a clearer view.

Some only have an est. 6 in wide strip of inner lining or none at all.

I want to know if an inner lining should exist or not?

Did the inner lining erode?

Is it a manufacture defect or faulty installation work?

I have attached my photos. You are welcome to use them on your
website if it can help someone. Perhaps, it could help someone
properly come to a conclusion and solution. Your assistance and help
would be greatly appreciated.
Sincerely, - A.G. 10/11/2012

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with an HVAC system, duct work, or often other more urgent building concerns that an owner or occupant may not have noticed. That said, I have taken a look at your photos and from what I can see:

There appears to be a partial omission of a complete (full surface coverage) plastic or vinyl liner inside sections of the flex-duct that you photographed, leaving what appears to be fibrous insulation, most likely fiberglass, exposed in the air path.

Some photos show the accumulation of dust inside the ductwork - normal and quite common in HVAC ducts and moreso when a rough surface is exposed to airflow through the system, and still moreso if the system does not make use of an adequate air filter at the return air inlet.

A closer examination might change this opinion, but from your photos there does not seem to be any sort of coating (as an alternative to an internal plastic liner) that reduces the pick-up of fiberglass into the airflow through this system. (There are other fiberglass duct products that make use of a surface coating to minimize fiber release.)

Yes, normally flex-duct used in HVAC systems includes a plastic or vinyl interior liner and an external cover as well, leaving the fiberglass duct insulation sandwiched between the two. In my OPINION and based on your pictures

It does not look as if the missing flex duct liner was due to mechanical damage - as I see that where no plastic liner is visible, there are straight edges along the apparently-missing liner - not something that would normally happen by a cleaning attempt for example; Nor is missing flex duct liner an installation defect, unless you want to argue that the installer should have noticed that the flex duct seemed peculiar and should have questioned its use.

Either this is an unfamiliar flex duct product (please send me photos of any product labels or markings for further research) that omits an interior liner, or it shows an unusual manufacturing method (perhaps an attempt at using coated fibers), or it is a manufacturing defect.

This duct work cannot be cleaned - which is often the case even with lined flex-duct as the material is fragile enough to be damaged by many mechanical cleaning processes;

It is possible (but by no means certain) that building air delivered through this system will have extra levels of fiberglass fragments. I opine that that result is not certain because we don't know the extent of actual mechanical damage to the exposed fiberglass (if any), we don't know if the fiberglass was coated to resist particle release, and we thus can't say what particles may be released into the air stream.

My recommendations for un-lined HVAC flex duct:

Do not attempt any mechanical cleaning of this flex duct as you would surely increase the fiber relase from it

Do replace readily-accessible flex duct sections that have fiberglass exposed on the duct interior or for that matter also any visibly damaged ductwork; Consider replacing all of it - a much greater cost if you have to remove flex-duct that is routed through walls or ceilings where it is not readily accessible;

Because replacing ductwork routed through inaccessible building cavities is very costly, you might ask a local HVAC duct service or cleaning company if they have experience using a spray-sealant on the interior of ductwork; in my OPINION this is a second choice to replacement because of the difficulty of accessing and coating all surfaces and because of the risk of a false sense of security that a problem has been "fixed" when it hasn't: we can't know that later the coating doesn't fall away. But the economics can make duct sealant coatings an attractive choice.

Make sure that air filters are properly installed and maintained in the system;

If there is an indoor dust complaint, consider testing the dust to see if the forensic lab traces significant levels of dust particles back to a sample of the duct insulation itself. For a simple inexpensive procedure to test house dust, see DUST SAMPLING PROCEDURE.

Question: six feet of damaged ductwork - health concerns?

I live in CA and had a new AC System installed about 7 years ago. I had it serviced by the company that installed it the first 5 years or so and they sold out to another company.
Since then I have used that company until the last service. The company that came out told me the first 5 or 6 six feet of my duct was the old original Fiberglass duct.

I didn't think much about it at the time, but I recently had my ducts cleaned. This company told me the same thing and advised me to contact the installing company.
They are now in AZ , and the company that took their clients won't respond to me.
I have been told this could be dangerous.
Can you tell me what government agency I would contact to see if there is anything I can do about it?
My wife and I and our two dogs all have bad allergies and it could be related.
Thank You for your response. - R.B. 3/24/2013

Reply:

RB,

I'm not sure what government agency is going to get involved in the case you described, though you might obtain some advice from your local health department. For some help in deciding if it is appropriate to hire an environmental expert to examine your home for allergens, mold, or other health risks that could contribute to the allergy complaints you cite, please take a look at MOLD EXPERT, WHEN TO HIRE.

Just from your description we can have no idea if the ducts are hazardous, or if so, in what form. Indeed if the ductwork was fiberglass lined and was mechanically damaged by improper cleaning it might make sense to replace it.

Replacing 6 feet of ductwork does not merit expensive testing, site analysis, etc. - the cost of such work would be far more than the cost of six feet of ducting.

...

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Technical Reviewers & References

Thanks to Mark Cramer, Tampa Florida, for assistance in technical review of the "Critical Defects"
section and for the photograph of the deteriorating gray Owens Corning flex duct in a hot attic. Mr. Cramer is a Florida home inspector and
home inspection educator.

Thanks to Jon Bolton, an ASHI, FABI, and otherwise certified Florida home inspector who provided photos of failing Goodman gray flex duct in a hot attic.

The Home Reference Book, a reference & inspection report product for building owners & inspectors.Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.

The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.

Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.

Thanks to Scott at SJM Inspect for suggesting this EPA document and for technical editing remarks regarding our air conditioning website,
SJM Inspection Service LLC, serves the entire state of CT, sjminspect.com 203-543-0447 or 203-877-4774
5/16/07

Thanks to reader Steven King for photographs and discussion of damaged ductwork, November/December 2010.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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